Removal of hydrocoumaric acid from acid nickel plating baths containing coumarin

ABSTRACT

COUMARIN (1,2 BENZOPYRONE) IS COMMONLY USED AS A LEVELER IN VARIOUS ACID NICKEL ELECTROPLATING BATHS, WHERE, DURING ELECTROLYSIS, THE COUMARIN UNDERGOES ELECTROCHEMICAL REDUCTION TO HYDROCOUMARIC ACID (2 HYDROXY PHENYL B PROPANIC ACID). AS THE CONCENTRATION OF HYDROCOUMARIC ACID IN THE BATH INCREASES, THE QUALITY OF THE NICKEL DEPOSIT IS ADVERSELY AFFECTED. THE PRESENT INVENTION DEALS WITH A METHOD OF REMOVING THE HYDROCOUMARIC ACID BY PASSING THE PLATING BATH SOLUTION THROUGH A BED OR COLUMN FILLED WITH A POLYMERIC SORBANT WHICH SELECTIVELY REMOVES THE HYDROCOUMARIC ACID AND COUMARIN FROM THE BATH. THE BED OR COLUMN IS THEN WASHED WITH AN ALKALINE MATERIAL SUCH AS NA2CO3 TO SELECTIVELY REMOVE THE HYDROCOUMARIC ACID FOLLOWED BY WASHING WITH A SOLVENT SUCH AS WARM WATER OR AN ORGANIC MATERIAL SUCH AS A LOW MOLECULAR WEIGHT ALIPHATIC ALCOHOL, ETHER AND KETONE IS DISSOLVE AND RECOVER THE COUMARIN. THE POLYMERIC SORBANT IS PREFERABLY NONIONIC AND IS TYPICALLY IN THE FORM OF SAMLL POROUS BEADS, EACH BEAD COMPOSED OF A LARGE NUMBER OF MICROSPHERES. THE METHOD IS ALSO APPLICABLE TO DERIVATIVES OF COURMARIN AND THE CORRESPONDING REDUCTION PRODUCTS THEREOF.

3,707,447 REMOVAL OF HYDROCOUMARIC ACID FROM ACID NICKEL PLATING BATHS CONTAIN- ING COUMARIN John William Alexander, Lyndhurst, Ohio, assignor to Kewanee Oil Company, Bryn Mawr, Pa. N Drawing. Filed Feb. 16, 1971, Ser. No. 115,706 Int. Cl. B01d 15/04; C23b /08, 5 /46 US. Cl. 204-49 12 Claims ABSTRACT OF THE DISCLOSURE Coumarin (1,2 benzopyrone) is commonly used as a leveler in various acid nickel electroplating baths, where, during electrolysis, the coumarin undergoes electrochemical reduction to hydrocoumaric acid (2 hydroxy phenyl B propanic acid). As the concentration of hydrocoumaric acid in the bath increases, the quality of the nickel deposit is adversely affected. The present invention deals with a method of removing the hydrocoumaric acid by passing the plating bath solution through a bed or column filled with a polymeric sorbant which selectively removes the hydrocoumaric acid and coumarin from the bath. The bed or column is then washed with an alkaline material such as Na CO to selectively remove the hydrocoumaric acid followed by washing with a solvent such as warm water or an organic material such as a low molecular weight aliphatic alcohol, ether and ketone to dissolve and recover the coumarin. The polymeric sorbant is preferably nonionic and is typically in the form of small porous beads, each bead composed of a large number of microspheres. The method is also applicable to derivatives of coumarin and the corresponding reduction products thereof.

BACKGROUND For many years acid nickel baths have been used for depositing a dull to bright plate on a suitable metallic or non-metallic substrate. There are a large variety of these acid nickel baths including sulfate baths, chloride baths, fluoroborate baths and sulfamate baths, all differing from one another in their basic composition, operating conditions, and the properties of the plated deposit. These acid baths are generally operated at a pH of between 2.5 and 5.5, a temperature in excess of 100 F. and a current density in the range of -150 amps per square foot (a.s.f.). One of the most common baths is a Watts bath which is composed of 3560 oz./ gal. of nickel sulfate hexahydrate, 4-6.5 oz./ga1. of boric acid and 5-12 oz./ gal. of nickel chloride hexahydrate. This bath is used at a current density of about 20-100 a.s.f. in the pH range of 4 to 5 and produces a dull finish.

Various properties of a nickel plating bath or the deposit obtained therefrom can be improved by the incorporation of various additives such as brighteners or leveling agents to the bath. One family of Widely used levelers consists of coumarin and its derivatives, the use of which are described in expired Pat. No. 2,635,076. This patent states that coumarin or its derivatives such as 4 methyl coumarin, 6-chlorocoumarin, etc. when used in an amount of 0.05 to 0.50 g./l. helps to produce a more level electroplate without sacrificing ductility, corrosion resistance or any of the other physical properties of the plate.

The chemical structure of coumarin, or 1,2 benzopyrone, is

United States Patent 0 Patented Dec. 26, 1972 During electrolysis of the bath some of the coumarin is electrochemically reduced to hydrocoumarin and then hydrolyzed to hydrocoumaric acid or 2 hydroxy phenyl propionic acid. As the hydrocoumaric acid builds up in the bath, there is a gradual deterioration in the quality of the deposit, particularly in the recesses of the plated object where the current density is low, and where the plate tends to become dark and spongy. Small amounts of hydrocoumaric acid, ranging up to 7 lbs./ gal. of plating bath can normally be tolerated. When the maximum allowable concentration is reached during an electroplating operation, the plating is halted and the bath is contacted with active carbon to remove the hydrocoumaric acid, along with the coumarin and other organic materials in the bath, after which this spent carbon is discarded because of the difiiculty of recovering the coumarin from the carbon. With the loss of the coumarin and other materials from the bath it is necessary to replace these materials, thereby adding to the cost of the electroplating operation.

BRIEF SUMMARY OF THE INVENTION These drawbacks are overcome according to the teachings of the present invention wherein one of the objects is the improved treatment of an acid nickel electroplating bath for the selective removal or control of hydrocoumaric acid.

Another object is a process which permits the continuous recirculation of a bath through a recovery unit wherein the hydrocoumaric acid is removed from the bath and the coumarin is recovered for reuse.

These and other objects are achieved in the manner to be hereinafter described in further detail, by passing a plating bath, containing an inimical amount of hydrocoumaric acid, though one or more beds of material having the capacity of selectively removing the coumarin and hydrocoumaric acid from the bath, followed by selective recovery of the coumarin substantially free of contamination by hydrocoumaric acid.

DETAILED DESCRIPTION OF THE INVENTION The harmful build-up of hydrocoumaric acid in an acid nickel electroplating bath is prevented by intimately contacting incremental portions of the plating bath with a suitable material capable of removing the coumarin and hydrocoumaric acid from the bath, and thereafter separately recovering the coumarine and hydrocoumaric acid from the material.

In more detail, hydrocoumaric acid is removed from an acid nickel plating bath by passing the plating solution through one or more beds or columns of resin, selectively removing the coumarin and hydrocoumaric acid from the bath by sorption on the resin and thereafter treating the resin to separately remove the hydrocoumaric acid and the coumarin and to regenerate the resin.

In a preferred embodiment of the invention, the resin is regenerated by eluting the hydrocoumaric acid from the resin with an alkaline material and removing the coumarin with a solvent. The alkaline material is preferably used as an aqueous solution of a basic salt or a hydroxide in the pH range of about 10 to 12. Exemplary of the alkaline salts that can be used are Na CO NaHCO K CO and NaBO while KOH, NH OH and NaOH are typical hydroxides that have been found to be useful. Any organic or inorganic solvent that readily dissolves the coumarin may be used to remove the coumarin from the resin, including warm water, 10w molecular weight straight and branched chain aliphatic alcohols, organic ethers such as ethyl ether, ketones such as acetone and methyl ethyl ketone, hydrocarbons, glycols such as Cellosolve and concentrated sulfuric acid. These solvents are preferably miscible in water to facilitate removal of the coumarin from the aqueous plating bath deposited within the pores of the resin.

Although the invention is directed primarily to conmarin and hydrocoumaric acid, it is also applicable to derivatives of coumarin wherein one or more of the hydrogen atoms on either of the two rings is replaced by an alkyl, acyl, methoxy, ethoxy, hydroxy methyl, hydroxy ethyl, chloro, hydroxy or carboxy groups. 4-methyl coumarin; 3-chloro coumarin; 3-acetyl coumarin; 6-chloro coumarin and 4,8-dimethyl coumarin are typical examples of these derivatives. During electrolysis of the bath, each of these chemical compounds undergoes a chemical reduction to produce hydrocoumaric acid or a derivative thereof.

Any material having the.unique capability of selectively removing coumarin and hydrocoumaric acid from an electroplating bath and from which these two compounds can be recovered, may be used in perfecting the teachings of the present invention. This material is typi cally hydrophobic and completely insoluble in the electroplating bath and should have 'suflicient structural strength and integrity to prevent packing in a column or bed. In addition it is preferably non-ionic and should have a highly porous structure. A product sold by Rohm & Haas under the name AXAD2 has been found to be a particularly suitable resin for the intended purpose. This material is a synthetic crosslinked co-polymeric resin composed of a major amount of polystyrene and a minor amount of divinylbenzene. The resin is in the form of hard spherical beads having an elfective diameter of .3 to .45 mm., each bead composed of a large number of microspheres. The beads have a porosity (ml. pore/ml. bead) of between .40 and .45 and a surface area in the range of 290/330 m. /gm. They are very hydrophobic, have good physical durability and do not contract or expand in use. Typically this AXAD2 resin can absorb up to about 20% of its weight of hydrocoumaric acid and coumarin, after which further sorption proceeds with diificulty. The hydrophobic portion of each molecule of hydrocoumaric acid and coumarin is selectively absorbed or otherwise held by resin, which, because it acts as a non-polar solvent, preferentially absorbs the coumarin rather than the hydrocoumaric acid. The resin can be used in a single packed column or a plurality of columns arranged in series or in parallel and is packed so as to avoid dead spaces in each column and channeling and cross diffusion of the plating bath passing through the column.

In practicing the present invention, the plating solution from which the hydrocoumaric acid is to be removed is typically flowed through a packed bed or column of the resin and is either returned directly to the plating tank or to a separate container Where it is collected for reuse. At the completion of the cycle the bed is washed with cold water to remove remaining traces of the plating bath after which an aqueous solution of sodium carbonate or other alkaline material such as sodium hydroxide is passed through the bed. This material preferentially solubilizes and removes the hydrocoumaric acid from the bed, while the coumarin remains sorbed on the surface of the resin. Coumarin is relatively non-polar while the hydrocoumaric acid is polar, at or above a pH of about 7 where it is in the phenol form 4 and becomes even more polar at a pH of 8.5 or above due to the conversion of the acid from the phenol form to the phenolate form The greater polarity increases the solubility of the hydrocoumaric acid and causes it to readily go into solution while the coumarin remains adsorbed on the resin. Washing of the bed with the alkaline solution is continued until the hydrocoumaric acid is effectively removed from the resin as can be determined by suitable analytical techniques.

When sodium carbonate is used to elute the hydrocoumaric acid from the bed, it is typically used in a concentration between 0.1% and 10% or higher if desired. The rate of elution of the hydrocoumaric acid is normally increased by increasing the concentration of the carbonate. However, this is not a linear relationship and at these greater concentrations, the cost of the carbonate becomes a drawback. The maximum permissible concentration is dictated by the solubility of the Na CO in water, and this is a function of temperature. For instance, between the temperatures of 0 C. and 104 C. respectively, the solubility of the salt varies from 7 parts to 48 parts per parts of Water.

A hydroxide such as a 0.025% sodium hydroxide solution having a calculated pH of 11.8 can be used to selectively remove the hydrocoumaric acid from the resin bed without removal of the coumarin. At a concentration of 0.1%, the pH of NaOH is about 12.4 and the coumarin is slightly soluble. With a 1% NaOH solution, the calculated pH is about 13.5 and the coumarin is readily soluble. Accordingly the pH should not exceed about 12 and should preferably be in the range of between about 10 and 12 in order to insure selective removal of the hydrocoumaric acid from the resin without removal of coumarin.

After all of the hydrocoumaric acid has been removed, the bed of resin is washed with cold water to remove excess alkali followed by washing with a suitable solvent such as warm water or preferably a low molecular weight aliphatic alcohol such as methyl or ethyl alcohol to remove the coumarin. The coumarin is quite soluble in the alcohol, particularly when the alcohol is used in a concentration of 80% or greater, and can readily be removed from the bed of resin. The eluate, or outgoing stream, containing the solvent and the coumarin is generally sufficiently free of hydrocoumaric acid to permit it to be returned directly to the plating bath where most of the alcohol is vaporized off at the operating temperature of the bath. The alcohol is quite effective in removing the coumarin from the bed of resin for at least two reasons; (1) the alcohol competes with and replaces the coumarin on the adsorption sites of the resin, and (2) the alcohol tends to solubilize the coumarin. For these reasons, the force of adsorption between the resin and coumarin are overcome and the coumarin is desorbed from the resin. After all or most of the coumarin has been eluted from the resin, the resin is again water washed to complete the cycle and is then ready for reuse.

Under certain circumstances, it has been found desirable to use warm Water, rather than alcohol, to remove the coumarin from the resin. The solubility of coumarin in water is a function of temperature and is sufficiently great in warm water to justify the use of water, heated to a temperature of at least F., to remove the coumarin from the resin. Furthermore, the coumarin is much more soluble in water than it is in the plating solution pre ent in the pores of the resin. For example, the solubility at room temperature is about .6 g./l. in a Watts solution and about 2.0 g./l. in water. The elution is preferably carried out by flowing the water through the bed of resin in an opposite direction to that of the plating bath which had been passed therethrough. Because of the large quantities of water that are necessary to remove the coumarin from the bed, the eluate is generally discarded inasmuch as it is usually too dilute to return directly to the electroplating tanks. Instead of water, a warm dilute alcohol solution may be used to elute the coumarin from the resin.

In a further embodiment of the present invention, a column or bed of resin is used to remove the hydrocoumaric acid and coumarin from the plating bath after which the column or bed is washed with two alkaline solutions to separately elute the hydrocoumaric acid and the coumarin from the resin. First, the resin is washed with an alkaline solution having a pH of less than 12 (e.g. .025% NaOH solution). The coumarin is very insoluble at this pH, and thus remains on the resin as the hydrocoumaric acid is removed. The resin is then washed with a more concentrated alkaline solution at a pH above 12 (e.g. a 1% solution of NaOH) to remove the coumarin.

Still another approach makes use of the fact that a resin such as A-XAD2, being a non-ionic resin, preferentially absorbs the coumarin rather than the hydrocoumaric acid. Two columns or beds, each packed with the resin, are joined to one another in series, and an acid nickel plating bath is passed sequentially therethrough. As the bath passes through the first column, the coumarin and hydrocoumaric acid compete for adsorption sites on the resin, but the coumarin is more readily adsorbed. As the bath continues on through the first column or bed and becomes depleted of coumarin, the resin then removes some of the hydrocoumaric acid from the bath. The remainder of the hydrocoumaric acid is absorbed as the bath passes through the second column. As additional plating bath is passed through the first column, the coumarin competes with and replaces the hydrocoumaric acid absorbed on the resin, after which the hycrocoumaric acid flows into the second column and is adsorbed. Eventually, the first column is substantially saturated with coumarin after which it can be regenerated by use of any of the fOrementioned techniques for removing coumarin from the resin, such as backwashing with methyl alcohol or warm water. The second column can be treated with a dilute alkali to remove the hydrocoumaric acid and to regenerate the resin in the second column. As yet another alternative, the second column or bed can contain or be composed of a material such as activated carbon which can be discarded after it has become saturated with hydrocoumaric acid.

The following examples are presented as a further elaboration of the teaching of the present invention, but without the intention of in any way limiting the scope thereof.

EXAMPLE I One liter of a nickel sulfate plating solution containing .223 gram of coumarin and 1.02 grams of hydrocoumaric acid was passed at a flow rate of about 200 ml./ hr. through a narrow glass U-tube containing a bed comprising 9.2 grams of dry A-XAD-2 resin. The eflluent stream was analyzed to determine the amount of coumarin and hydrocoumaric acid passing through the tube and the results showed that all of the coumarin and 80% of hydrocoumaric acid originally in the bath were retained on the resin.

The U-tube was washed in the same direction of flow with 228 ml. of water at room temperature to remove the nickel salts followed by washing with 287 ml. of a 1% sodium carbonate solution (calculated pH of 11.4). It was determined that both of the washings selectively removed substantially all of the hydrocoumaric acid from the resin. The sodium carbonate was washed from the column with cool water after which 125 ml. of pure methyl alcohol, was passed through the U-tube and the eluate was collected, and was analyzed for coumarin. It was found that the alcohol removed virtually all of the coumarin from the resin. 1

6 EXAMPLE II A saturated solution of coumarin in a Watts bath composed of 260 g./l. of nickel sulfate hexahydrate, 45 g./l. of nickel chloride hexahydrate and 45 g./l. of boric acid in 1 liter of bath was prepared containing .686 g. l. of coumarin. 200 ml. of the Watts bath was passed through 9 grams of A-XAD-2 resin in the bend of a glass U-tube to collect .137 gram of coumarin. 141 ml. of water at about 26 C. Was then passed through the U-tube in the reverse direction and the eluate was then collected in 3 ml. increments which were analyzed for coumarin. The concentration of coumarin reached a peak of .423 g./l. with the eighth increment. The bend of the U-tube was then immersed in boiling water and 250 ml. of water was passed through the tube, in the same direction as before, and was collected in 3 ml. increments. Each increment of eluate was analyzed for coumarin and a maximum concentration of .894 g./l. was realized in the eleventh increment. In all, 86% of the coumarin was removed from the U-tube by reverse flow of water through the tube with the warm water being much more effective than the cool. water. However, the concentration of the coumarin in the water was too small to warrant addition of the eluate to the plating bath.

EXAMPLE III In this experiment a continuous method was used for removing hydrocoumaric acid and recovering the coumarin from an operating nickel Watts bath. Two vertical glass columns each having an inner diameter of A1" and height of 10" were used in parallel to continuously remove the hydrocoumaric acid from a 9 liter bath, each column containing 21 grams of A-XAD-2 resin. During the trial, one column underwent regeneration while the other column was being used to purify the bath. T0 9 liters of the Watts bath of Example II, 1.80 g. of coumarin was added to establish a concentration of 0.20 g. per liter. The pH of the solution was adjusted to a value of 4.0 and was maintained at this pH by the addition of H 50 as necessary during the course of the plating. The temperature of the plating bath was held at 51 and the bath was agitated by a flow of air of about 450 cc. per minute dispersed in the bath below the cathode. A 2" x 4" steel panel was immersed in the bath and electroplated at 3 amps using nickel anodes on each side of the panel.

The plating was continued for 48 hours after which the solution was found to contain 0.031 g. per liter of coumarin and .159 g. per liter of hydrocoumaric acid. The level of coumarin was again raised to 0.20 g. per liter by the addition of fresh coumarin. The plating was continued for an additional 6 hours, during which time more coumarin was added and the solution was passed through the first column at a rate of 6 ml. per minute with the efiluent being returned to the bath. At the end of the 6 hours, the bath was analyzed and found to contain 0.30 g. per liter of coumarin and 0.234 g. per liter of hydrocoumaric acid.

The flow of the plating bath was switched to the second column and was increased to 25 ml. per minute. In subsequent cycles the flow varied from 20 to 25 ml. per minute and total flow time through each column varied from 46 hours.

Regeneration of each column was carried out by first removing the hydrocoumaric acid and then the coumarin. The first step in the regeneration involved water washing to remove the nickel plating solution from the column. This solution was returned to the bath as long as it remained deep green indicating that it contained substantial amounts of nickel salts. The column was then washed with 500 ml. of additional water which was collected and analyzed for coumarin and hydrocoumaric acid. It contained virtually no coumarin but contained as much as 0.3 g./l. of hydrocoumaric acid. The remaining hydrocoumaric acid was then removed by washing with 1.0 liter of 1% Na CO solution. Incremental portions of this solution contained over 0.6 g. of hydrocoumaric acid per liter. The column was again washed with about 50 ml. of water followed by 150 ml. of .0l% H 80 to remove the'remaining alkali from the resin. The above steps were carried out with a moderately rapid flow rate of 25 to 50 ml. per minute. The column was then washed with 100 ml. of undiluted methanol in reverse flow at about ml. per minute to remove coumarin from the resin followed by 50 ml. of water to wash out the methanol. The resin was then ready for the next cycle.

The plating bath was periodically analyzed for coumarin and hydrocoumaric acid. Coumarin was added to keep the concentration at about .2 g. per liter. Recovered solutions for the first five regeneration cycles were also analyzed for coumarin and hydrocoumaric acid. The vol umes of these solutions were recorded to give the balance of additions and recoveries. Methanol solutions of recovered coumarin were returned to the plating solution. The process was continued for an additional ten cycles during which only periodic analysis of the plating solution was carried out. The recovered coumarin was returned to the bath as before. During the course of this operation the level of hydrocoumaric acid in the plating bath was maintained between 0.18 and .23 g. per liter and was 0.192 g. per liter at the end of this trial.

EXAMPLE IV In another embodiment of the present invention, two glass columns, the first containing about grams of dry A-XAD-2 resin and the second with about 50 grams of dry resin were connected in series after which about 8 liters of an acid nickel plating solution containing about .33 g./l. of coumarin and about .65 g./l. of hydrocoumaric acid was passed through the two columns at a rate of 6 mL/minute.

As the plating bath was passed through the first column of resin, the coumarin and hydrocoumaric acid competed for the sorption sites on the resin. The resin being non-ionic, preferentially sorbed the less polar coumarin, after which the hydrocoumaric acid was sorbed on the remaining sites. Accordingly, during the initial portion of the adsorption cycle, the concentration of coumarin on the resin at the inlet was high and gradually decreased along the length of the column while the concentration of the hydrocoumaric acid becomes greater toward the outlet of the first column. As additional plating solution was passed through the first column, the hydrocoumaric acid on the resin was gradually replaced by coumarin until the first bed was saturated with coumarin. The hydrocoumaric acid which was first sorbed and then desorbed then passed into the second column where it was again sorbed by the resin.

The first column adsorbed more than 90% of the coumarin and less than of the hydrocoumaric acid while the second column reduced the level of hydrocoumaric acid to about .20 g./ 1., an acceptable level for all plating operations, and removed nearly all of the remaining coumarin from the bath.

The smaller first column was then washed in the reverse direction at a rate of 6 ml./min. with 1734 ml. of hot water maintained near the boiling point to recover about 85% of the coumarin from the resin and the eluate was returned to the plating bath to restore some. of the coumarin that'had been removed.

The larger second column was regenerated by washing with a 1.0% NaOH solution and the eluate, containing coumarin and hydrocoumaric acid, was discarded.

These results indicated that one gram of this dry resin (AXAD-2) is capable of adsorbing about .2 gm. of the coumarin and hydrocoumaric acid. With this information and with knowledge of the amount of coumarin used and the maximum permissible concentration of hydrocoumaric acid in the bath, the size of the two columns can be readily determined. The first column should be only large enough to adsorb all or nearly all of the coumarin while the second column should be used primarily for removal of hydrocoumaric acid. Within this framework, there are several variations that can be made from the procedure described in Example 4 without departing from the spirit or scope of the present invention. For example:

(a) The first column can be washed with any of the previously mentioned organic or inorganic solvents such as warm dilute methyl alcohol or 1% NaOH solution to recover the coumarin from the resin,

(b) The second column can be washed in two steps to separately remove the hydrocoumaric acid and coumarin as previously described,

(c) The two separate columns can be replaced by a single long column provided with means for separately backwashing the upper portion of the column to remove coumarin and washing the lower portion to remove the hydrocoumaric acid, or v (d) The second column can be packed with activated carbon such as CAL granular carbon sold by the Pittsburgh Activated Carbon Division of Calgon Corp. instead of the resin to adsorb the hydrocoumaric acid after which the carbon can either be regenerated by appropriate means or discarded.

EXAMPLE V In another experiment, 5 liters of a Watts nickel plating bath was passed through a single glass column containing about 20 grams of A-XAD-2 resin. The bath initially contained about .20 g./l. of coumarin and about .45 g./l. of hydrocoumaric acid, most of Which was adsorbed by the resin. The column was washed with cold water to remove the salts of the plating bath after which about ml. of a 0.025% solution of NaOH was passed through the column in the same direction of flow as the bath to dissolve and remove the hydrocoumaric acid. The column was then washed with 150 ml. of a 1% solution of NaOH to remove more than 95% of the coumarin.

EXAMPLE VI In a further embodiment of this invention, a bed of resin on which about equal amounts of coumarin and hydrocoumaric acid were adsorbed was washed in a concurrent direction with a 50% solution of methyl alcohol to remove the hydrocoumaric acid after which the bed was backwashed with undiluted warm F.) methyl alcohol to remove more than 90% of the coumarin along with remaining traces of hydrocoumaric acid. This second eluate was returned directly to the plating bath.

Although the invention has been described in terms of a specific non-ionic resin, it should be understood that any other resin or non-resinous material having the capability of removing hydrocoumaric acid from the plating bath by absorption and adsorption and which can be regenerated by desorption may be used. vFor example Amberlite XAD-4, a resin sold by Rohm & Haas, is chemically similar to A-XAD-Z, has a surface area of about 750 m. gm. and can be substituted for the A-XAD-Z.

Other modifications can be made in practicing the present invention without departing from the scope thereof which is described in the claims, in which I claim:

1. In a nickel electroplating method using an aqueous acid nickel electroplating bath containing an addition agent selected from the group consisting of coumarin, and derivatives of coumarin in which one or more of the, hy-

drogen atoms on'either of the two rings is replaced by one or more of an alkyl, acyl, methoxy, ethoxy, hydroxy methyl, hydroxy ethyl, chloro, hydroxy or carboxy groups,

therefrom, and (b) thereafter separately removing the addition agent and the conversion product from the copolymer.

2. The method of claim 1 wherein the additive and the conversion product are removed by passing the bath through a bed containing the polymer.

3. The method according to claim 2 wherein the conversion product is removed from the polymer by washing the polymer with an aqueous solution of an alkaline material.

4. The method according to claim 3 wherein the addition agent is thereafter removed from the polymer by washing the polymer with a solvent.

5. The process of claim 2 wherein the bath is passed through an elongated column packed with the polymer.

6. The method of claim 1 wherein the bath is passed successively through two columns in series each containing the polymer.

7. The method according to claim 6 wherein the polymer in the first column is washed with a solvent to remove a substantial amount of the additive therefrom and the polymer in the second column is treated with an alkaline material to remove a substantial amount of the conversion product therefrom.

8. The method of claim 1 wherein the resinous copolymer is washed with an alkaline solution having a pH of between 10.0 and 12.0 to selectively remove the conversion product therefrom.

9. The method of claim 8 wherein the alkaline solution is an aqueous solution comprising a compound selected from the group consisting of sodium hydroxide, ammonium hydroxide, sodium borate, sodium carbonate, sodium bicarbonate and potassium carbonate.

10. The method of claim 1 wherein the additive is selectively removed by washing the compolymer with a solvent for the addition agent.

11. The method of claim 10 wherein the solvent is selected from the group consisting of low molecular weight aliphatic alcohols, ketones, esters, glycols, solutions of inorganic hydroxides having a concentration of greater than about 0.5% and less than about 1% and a pH above 12, and water at a temperature of at least 140 F.

12. The method of claim 1 wherein the resinous copolymer comprises a major amount of polystyrene and a minor amount of divinylbenzene, said co-polymer in the form of discrete beads having a size of between 20 and mesh, each bead forming a porous agglomerate of a large number of smaller beads.

References Cited UNITED STATES PATENTS 3,531,463 9/1970 Gustafson 2103O X 3,414,491 12/1968 DuRose et al. 204-49 GERALD L. KAPLAN, Primary Examiner US. Cl. X.R.

2lO-30; 260343.2 R, 521 R 

